The facts and the myths about Swanwick's screens

Despite denials from National Air Traffic Services, the trade union, the Civil Aviation Authority and the Government, some controllers insist that the readability of their computer screens is a safety issue. Tony Collins reports

On television last week a spokesman for the air traffic controllers' union Prospect gave comforting assurances about the safety of computer screens used by controllers at the £623m Swanwick centre in Hampshire. He did so after Computer Weekly's disclosure of the contents of official forms in which controllers had recorded difficulties reading their computer screens.

In one case a controller had submitted an ATC/024 Operational and Safety Observation Report form - a discretionary extra report on safety issues - after he repeatedly misread the height of aircraft by thousands of feet.

Another form reported a controller had "co-ordinated the aircraft into the incorrect [air space] sector. A third reported another controller had "initially co-ordinated" flight AIH978, bound for Glasgow, to Cardiff because of the similarity of the cities' codes - EFPF and EGFF respectively.

A further report form showed a controller had passed wrong identification information to another airspace sector because of "lack of clarity on full flight plan". He had misread "94E as 54E", while a fifth showed a controller mistook a number "8" for a "6" on the flight plan. "Even moving my head closer to the screen only marginally improved the digit", the form said. He considered the matter safety-related because it could have resulted in an "operational wrong decision".

None of the mistakes developed into an incident, partly because they were spotted in time, although all of the safety observations were endorsed by the controller and the watch manager or supervisor as "safety related".

All of the mistakes have arisen since the Swanwick systems became operational in January, after nearly six years of delays.

Safety observation reports would not normally be publicised but the frustration of some "planner" controllers about the clarity of their screens has been compounded by what they see as an inability to persuade anyone in authority to take remedial action.

In the House of Commons last Thursday, the day when the latest disclosures were published in Computer Weekly, Robin Cook, the Leader of the Commons, said, "With regard to this morning's claims about Nats [National Air Traffic Services] operators misreading heights of planes and being unable to read their new displays, Nats completely rejects those allegations."

He added that Nats was "confident that nothing has happened to put the safety of passengers at risk".

The union, Prospect, and the safety regulator the Civil Aviation Authority (CAA) also rejected the claims that unclear screens impinge on the safety of passengers. Each cited the other in justifying its position. Prospect, for example, said the screens were safe because the CAA's Safety Regulation Group has certified the Swanwick system as safe, while in a letter to Computer Weekly this week, the CAA's Safety Regulation Group said its assessment of the system was backed by Prospect.

A union spokesman explained in a TV news report why unclear screens do not, in his view, present any issue related directly to air safety. "The screens we are talking about are the planning screens not the radar screens that most people would associate with air traffic controllers," he said. The tone of his statement was so reassuring that the television reporter wrongly introduced him as an official Nats spokesman.

But some controllers wonder whether the union, the CAA, Nats and the Government are giving assurances on safety to avoid alarming travellers. Until this week the CAA had said that as planner controllers do not do any job related to the safety of aircraft the legibility of their screens cannot compromise safety. But it has now altered its position slightly. In this week's letter to Computer Weekly it says the displays do not present a "safety-significant" risk.

Controllers say, however, that their quest to highlight what they regard as a risk to safety is being clouded by a series of misleading statements. These have given the impression that planner controllers are not bone-fide air traffic controllers.

For example, the Daily Telegraph reported last week that the planner controller's job was to "undertake preparatory work to estimate the most efficient routes for flights". But planner controllers' licence conditions require that they maintain separation between aircraft. They do not have direct radio contact with pilots - this is the remit of "tactical" controllers - but planners handle the transfer of aircraft from one airspace sector to another.

Looking at radar and other information on their screens, they accept or reject an aircraft that is offered to them by a planner controller in an adjacent airspace sector. If they believe a conflict in aircraft paths could arise, they will reject an aircraft offered into their sector and will suggest a different height. The tactical controller will then instruct pilots to alter their height to accommodate the requirements of the planner controller.

No single wrong decision or misreading of a screen by a planner controller should, in itself, compromise safety. But controllers say that a disaster is usually caused by a chain of wrong decisions, events and/or technical problems that in themselves seem inconsequential. The Paddington rail crash, for example, was ostensibly caused by a driver failing to see a red light, but drivers had warned before that the red light was difficult to see.

In the case of Swanwick, controllers maintain that they warned repeatedly during the system's 10-year development that the screens were difficult to read, but they say that their concerns were belittled.

They now have an influential supporter, however. The Health and Safety Executive (HSE) appears to disagree with Nats, Prospect and the CAA on the question of safety.

In a letter which said the screens appeared to breach legislation, the executive said that "these design deficiencies [relating to the screens] may have implications in relation to air safety". For this reason the HSE copied its letter to the CAA's Safety Regulation Group.

In 1999, an audit report, initiated by the House of Commons transport committee, criticised Nats' approach to "bad news". The report, by consultancy Arthur D Little, found that there had been an "an unwillingness to face up to and discuss bad news" and a "style which inhibited an open and frank discussion of difficult problems". The firm said it believed that the "whole culture and environment" was a contributor to weaknesses in "picking up on major issues" relating to the Swanwick systems.

Nats said it has now swept away the old culture of defensiveness and picked up the issue of some screens being unclear. It plans some changes to displays, although it is not clear what the modifications will be, and whether these will address all of the concerns.

Prospect also faces a challenge. Some controllers have sought legal advice on whether they can be held to blame if they misread an unclear screen and this contributes to a near miss or accident. A top QC, Ian Croxford, produced a 16-page report concluding that Prospect would be abdicating its duty if it "fails to protect [air traffic controller] members before there is a tragedy".

Make it easy on your eyes Some computer experts say the legibility of characters and numbers on screens may have as much to do with the choice of font and typeface as the quality of hardware.

After last week's disclosures about the unclear screens at the Swanwick air traffic control centre, Computer Weekly was given details of a new typeface designed by John Gill, chief scientist at the Royal National Institute for the Blind, and the Digital Television Group which represents dozens of TV companies. They have devised a font expressly for use with display systems to avoid legibility problems.

The font is called Tiresias Screen font, devised initially to make subtitles more legible for digital terrestrial television.

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